The detection of a radiation emanating from a tracer flare of a flying body, by means of a point detector and evaluation of the measured signals in an evaluating electronic means is known from the German Patent Publication No. 2,944,261. The detector system in the known device serves for guiding the flying body along an optical axis. The known methods of steering flying bodies use detectors which essentially function in the infrared range. In the German Patent Publication No. 2,944,261 the point detector is supposed to measure the intensity of a radiation largely independently of the spectral range. For measuring the intensity, modulation signals are generated by means of a modulator disk out of consecutive impulses following one another without interruption. Only the modulated signal is then processed in the evaluating electronic circuitry for separating the flying body tracer flare from interference radiators.